Method and apparatus for validating documents by spectral analysis of light reflected therefrom



Nov. 25. 1969 D. R. AUimERHEiDE 3,480,185

METHOD AND APPARATUS FOR VALIDATING DOCUMENTS BY SPECTRAL ANALYSIS OF LIGHT REFLECTED THEREFROM Filed July 26. 1965 5 Sheets-Sheet l s G e O 0 O .0 0 O @906 49 a5 44 22 24 46 V L I V A], 20 Z/ 39 2b 42 /4 --2 :32 Q fin cantor:

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by MW Nov. 25. 1969 D. R. AUFDERHEIDE METHOD AND APPARATUS FOR VALIDATING DOCUMENTS BY SPECTRAL ANALYSIS OF LIGHT REFLECTED THEREFROM 5 Sheets-Sheet 2 Filed July 26, 1965 ms mm Nov. 25. 1969 o. R. AUFDERHEIDE METHOD AND APPARATUS FOR VALIDATING DOCUMENTS BY SPECTRAL ANALYSIS OF LIGHT REFLECTED THE REFROM Filed July 26, 1965 5 Sheets-Sheet Nov. 25. 1969 D. R. AUFDERHEIDE METHOD AND APPARATUS FOR VALIDATING DOCUMENTS BY SPECTRAL ANALYSIS OF LIGHT REFLECTED THEREFRQM 5 Sheets-Sheet 5 Filed July 26, 1965 United States Patent 3,480,785 METHOD AND APPARATUS FOR VALIDATING DOCUMENTS BY SPECTRAL ANALYSIS OF LIGHT REFLECTED THEREFROM Don R. Aufderheide, Indianapolis, Ind., assignor to Vendit, Inc., Anderson, Ind., a corporation of Indiana Filed July 26, 1965, Ser. No. 474,785 Int. Cl. G01n 21/30 U.S. Cl. 250219 20 Claims ABSTRACT OF THE DISCLOSURE A method and apparatus for discriminating between desired and undesired documents which employs a plurality of narrow band light sources each emitting light in a different color spectra, the light sources being sequentially illuminated, one at a time. The document to be inspected is positioned to receive light from the light sources and a plurality of sensors are positioned to receive light reflected from preselected discrete areas on one surface of the document and to provide signals in response to the spectral content thereof. Such signals must be within predetermined limits for each sequential color emission.

This invention relates generally to a method and apparatus for validating documents, i.e., for discriminating between desired and undesired documents such as paper currency, and more particularly to a method and apparatus for discriminating between desired and undesired documents by spectral analysis of light reflected from a surface of the document being inspected.

Various methods and apparatus have been proposed for discriminating between desired and undesired paper currecny, the most common application for such apparatus being for making change and/or actuating a vending machine. In one common type of such apparatus, discrimination is provided by light-responsive cells underlying different areas of the currency and respectively responding to the quantity of light transmitted through those areas. This apparatus, however, provides minimum response to color variation in the ink and paper since the transmission of the light through the currency largely desensitizes any color effects in the transmitted light impinging upon the light-responsive cells.

It has been found that discrimination between acceptable and unacceptable documents, particularly paper currency, can be accomplished with great accuracy by analysis of the spectral content of light reflected from a plurality of preselected discrete areas of the document. With such a method, not only is the intensity of the light reflected from a given discrete area on one surface of a document responsive to the mechanical characteristics of the printing, but also the spectral content of the reflected light depends upon the background color, the color of the ink and the mechanical characteristics of the printing, each of these characteristics contributing its own spectral characteristics.

In application serial No. 375, 412, now Patent No. 3,220,549 of Lan I. Wong, assigned to the assignee of the present application, a method and apparatus is disclosed for discriminating between desired and undesired documents by special analysis of reflected light in which a broad band light source and narrow band reflected light sensors are employed. It has been found, however, that still more accurate discrimination is obtainable by the employment of several narrow band light sources each emitting light in a different color spectra or sec- 3,480,785 Patented Nov. 25, 1969 ice tion, these light sources being sequentially illuminated one at a time. With this method and apparatus, the signals provided by the sensors in response to light reflected from the preselected discrete areas on one surface of the document being inspected must be within predetermined limits for each sequential color emission, thus providing substantially improved discrimination.

It is accordingly an object of the invention to provide an improved method for discriminating between desired and undesired documents by spectral analysis of light reflected therefrom.

Another object of the invention is to provide improved apparatus for discriminating between desired and undesired documents by spectral analysis of light reflected therefrom.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a schematic cross-sectional view of apparatus in accordance with the invention;

FIG. 2 is a fragmentary, schematic view in perspective further illustrating the apparatus of the invention;

FIG. 3 is a fragmentary, cross-sectional view showing the sensors employed in the apparatus of the invention;

FIG. 4 is a diagram schematically illustrating the electrical system of the invention;

FIG. 5 is a fragmentary, schematic diagram showing one specific embodiment of the logic relays of the system of FIG. 4;

FIGS. 6 and 7 are diagrams useful in explaining the operation of the system of FIG. 4; and

FIG. 8 is a flow chart illustrating the method of the invention.

Referring now to FIGS. 1, 2 and 3 of the drawings, there is shown a paper currency validation apparatus, generally indicated at 10, which may be used in conjunction with conventional coin dispensing apparatus (not shown) to provide a bill changer, and/ or in conjunction with conventional vending apparatus (also now shown). The currency validation apparatus 10 comprises an onclosing housing 12 defining an interior 14. The front wall 16 of housing 12 has an opening 18 therein communicating with the interior 14 in which a bill-receiving slide 20 is positioned. Slide 20 is slidably mounted upon suitable horiozntally extending rails 21 for movement between a loading position outside of the housing 12, as shown in solid lines in FIG. 1, and a bill-inspection position within the interior .14 of housing 12, as shown in dashed lines in FIG. 1 and in solid lines in FIG. 2. Slide 20 has a shallow bill-receiving recess 22 formed in its upper surface for receiving and holding a bill 24 to be inspected. Slide 20 has a slot 26 formed in its rear edge 28 for a purpose to be hereinafter more fully described.

In the preferred embodiment of the invention, slide 20 is moved between its outer loading position, an shown in FIG. 1, and its inner inspection position as shown in FIG. 2 by means of a motor 30 which drives crank 32. Crank 32 is in turn connected to slide 20 by means of linkage 34 having a lost motion spring connection 36 therein. With this arrangement, the slide 20 engages stop 38 before the end of the stroke of crank 32, the spring 36 thus providing a finite dwell during which slide 20 is held stationary in its inspection position within housing 12.

In the preferred embodiment of the invention, a reference or standard piece of currency 40 is firmly secured to a support 42 within housing 12, the spectral response of the reference piece of currency 40 to reflected light being compared with the spectral response of the test piece of currency 24, as will be hereinafter more fully described.

A grabber assembly 44 is provided in the housing 12 comprising a fixed jaw 46 and a movable jaw 48 actuated by grabber solenoid 50. As the slide with the test bill 24 in the recess 22 thereof moves rearwardly to the inspection position, the lower movable jaw 48 of the grabber assembly 44 enters slot 26 of the slide 20 under the bill 24 while the upper fixed jaw 46 is disposed over the bill, as best seen in FIG. 2. If the bill has been validated, as will be hereinafter described, grabber solenoid is energized thus actuating the movable jaw 48 to clamp the bill 24 against upper jaw 46 and at the same time to lift the bill out of recess 22 and above rear edge 28 of slide 20. Thus, as slide 20 is moved forwardly to its loading position, bill 24 is withdrawn from the recess 22 and passes over rear edge 28. When the grabber solenoid 50 is deeriergized, the thus withdrawn bill 24 is released and falls into a collecting receptacle 52.

A plurality of light sources 54 is provided in the upper portion of the interior 14 of housing 12 disposed so that both the reference bill 40 and the test bill 24 in its inspection position equally and uniformly receive light therefrom. Each of the light sources 54 emits light in a discretely different narrow band color spectra or section. For accurate discrimination, it is considered desirable to employ at least three light sources emitting light in spaced regions of the spectrum, at least two of which are in the visible range. It is further considered desirable that the color spectra or sections emitted by the light sources 54 include color components existing on one surface of a desired document, i.e., a genuine piece of currency, it being understood that the color spectra or sections emitted are not limited to such color components. In the illustrated embodiment, light sources 54 comprise three flourescent lamps 56, 57, 58, F6T5 lamps having been found to be suitable. In the illustrated embodiment for use in validating United States paper currency and in which the green side of the bill is inspected, one of the lamps emits near ultraviolet light and has a peak at approximately 350 millicrons, one emits green light and has a peak at approximately 525 millicrons, and the remaining lamp emits pink light and has a peak at approximately 615 millicrons. It will be observed that the ultraviolet and green spectra or sections are color components appearing on the green side of United States paper currency. As will be hereinafter more fully described, the fluorescent lamps 56, 57, 58 are sequentially energized so as to provide sequential emission of light in the respectively different color spectra or sections, one at a time.

In the illustrated embodiment, an open mesh screen 60 is provided extending across interior 14 of the housing 12 between the light sources 54 and the test and reference bills 24, 40. Screen 60 supports two groups 62, -64 of photosensitive devices or sensors which may be conventional relatively broad band photocells. Use of the screen 60 permits the two groups of photocells 62, 64 to be disposed in a wide variety of predetermined arrangements or patterns so as to view preselected discrete areas on the test and reference bills 24, 40; however, as will be hereinafter more fully described, the two groups 62, 64 are arranged in the same pattern so as to view corresponding discrete areas of the two bills. In order to confine the field of view of the photocells so that the respective discrete areas viewed are relatively small with reference to the total area of the test and reference bills 24, 40, each of the photocells 66 is disposed within a tubular defining sleeve 68, as best seen in FIG. 3.

In the illustrated embodiment, the group 62 of photocells comprises three photocells 70, 71, 72 respectively arranged to view preselected spaced-apart discrete areas 73, 74, 75 on the surface of the reference bill 40. It will thus be understood that the light emission provided by the light sources 54 is reflected from the surface of the reference bill 40 and that portion which is reflected from the discrete areas 73, 74, 75 is respectively received by the photocells 70, 71, 72 as indicated by the dashed lines 76.

Group 64 likewise comprises three photocells 77, 78, 7? respectively arranged to view discrete areas 81, 82, 83 on the surface of the test bill 24 when in its inspection position. The locations of the photocells 77, 78, 79 of the group 64 and the locations of the discrete areas 81, 82, 83 on the test bill 24 correspond respectively to the locations of the photocells 70, 71, 72 of group 62 and discrete areas 73, '74, 75 on the reference bill 40.

It will be readily understood that the employment of a greater number of sensors in each group 62, 64 and/or the employment of a greater number of light sources 54 will provide still more accurate discrimination, while a fewer number of sensors and/or light sources will provide less expensive apparatus with somewhat reduced discrimination. However, the employment of three sensors in each group 62, 64 and the employment of three light sources sequentially emitting different colored light has been found to provide highly accurate discrimination for validating United States paper currency. The discrete areas on the reference and test bills which are respectively viewed by the photocells of groups 62, 64 are perfera'bly chosen to provide different spectral response. Thus, in the case of a one dollar United States bill, areas 73, 81 may be in the region of the pyramid on the green side of the bill, areas 74, 82 may be within the white area under the letter N, and areas 75, 83 may be on the shield portion of the great seal of the United States, each of these areas having different engraving and different amounts of green and thus providing a different spectral response.

The provision of the screen 60 for supporting the photocells of groups 62, 64 permits the locations of the photocells to be changed, either from time to time in any given apparatus, or between one apparatus and another, thus inhibiting pilfering. It will be readily understood that other arrangements for adjustably mounting the photocells of groups 62, 64 may be employed, such as an arrangement to move each corresponding pair of photocells, such as 70, 77 in unison.

Another photosensitive device or sensor 85 is provided mounted on the screen 60 toward the front wall 16 of the housing 12. As will hereinafter be more fully described, the photocell 85 receives light reflected from an empty recess 22 of slide 20 when the slide is returned to its loading position, thus providing an indication that validation has been successfully completed and the bill removed by the grabber mechanism 44. As will be hereinafter described, the signal provided by the photocell 85 is employed to actuate the change-making and/or vending apparatus. Thus, even though a test bill 24 had successfully passed the validation test, failure of the grabber apparatus 44 properly to function or a successful effort to pilfer the validated bill would result in the bill remaining in the recess 22 as the slide 20 is returned to its loading position and thus in the absence of a signal provided by the photocell 85, no pay-out or vend signal, will be provided, as will hereinafter be described.

Referring now additionally to FIGS. 4 and 8 of the drawing, the drive motor 30 is connected for energization across supply lines 88 which are connected to any suitable source of energizing potential (not shown) by means of a momentary contact starting switch 90. Motor 30 drives a plurality of timing cams 86 and cam-actuated contact 86-1 is connected across the start switch 90. Thus, a validation cycle is initiated by momentary actuation of the start switch 90 which in turn energizes the motor 30 causing cam-actuated contacts 864 to close, thus sealingin the motor energizing circuit for one validation cycle; cam-actuated contacts 86-1 are opened by cams 86 at the end of one validation cycle, i.e., upon return of the slide 20 to its loading position.

Flonrescent lamps 56, 57 and 58 are respectively coupled across secondary winding 90 of transformer 92 by suitable ballast resistors 94, 95, 96, 97 and cam actuated contacts 86-2, 86-3, 86-4, 86-5. Primary Winding 98 of transformer 92 is adapted to be coupled to any suitable source (not shown) of alternating current energizing potential.

As above-described, the spring 36 in the linkage 32, 34 coupling the motor 30 to the slide 29 provides a dwell period for the slide in its inner inspection position during which the slide 20 and the test bill 24 therein are held stationary with respect to the light sources 54. During this interval in which the slide 20 is held stationary in its inspection position, cams 86 sequentially actuate contacts 86-2, 86-3, 86-4, thereby sequently to energize and thus illuminate lamps 56, 57, 58, one at a time. The illumination or flashing of each lamp 56, 57, 58 in succession is only for a sufficient length of time to provide a stable output in each of the sensing channels A, B, C, to be hereinafter more fully described, and in a specific embodiment of the invention, each of the flourescent lamps is flashed on for a period of approximately 400 milliseconds.

While the specific arrangement of the different colored lamps 56, 57, 58 is not critical, for the purposes of discussion of a system of FIG. 4, lamp 58 is considered to be near ultraviolet-emitting lamp. When the dwell or interval during which slide 20 is held stationary in its inspection position has been completed and motor has initiated return of the slide 20 to its outer or loading position, cams 86 actuate contacts 86-5 to connect the ultraviolet lamp 58 in series with ballast resistor 97 across the secondary winding of transformer 92, ballast resistor 97 having a lower value than resistor 96 so that lamp 58 is illuminated with increased brilliance. The empty tray sensor 85 and its amplifier are arranged so that an output signal is not provided when a bill 24 remains in the recess 22 of slide 20 when the slide is returned to its loading position. Tray 20 is preferably formed of polished metal and thus, when the recess 22 is empty as the slide is returned, fishing of the ultraviolet lamp 58 with greater brillance in response to actuation of cam contacts 86-5 will provide a sufiicient output from the photocell 85 and amplifier 100 to provide an output signal in output circuit 102 of amplifier 100, as will be hereinafter described. In order to View the entire area of the empty slide, it may be desirable to employ two or more empty tray sensors 85.

Each of the discriminator channels, A, B, and C respectively associated with corresponding pairs of photocells 70 and 77, 71 and 78, 72 and 79, is identical, and thus only channel A associated with corresponding photocells 70, 77 will be described in detail. Each of the corresponding pairs of photocells 70 and 77, 71 and 78, 72 and 79 is coupled in a bridge circuit 104; the bridge circuit 104 is energized by secondary winding 106 of transformer 108 having its primary 110 coupled across a suitable source (not shown) of higher frequency alternating current, such as 2000 cycles. Fixed resistors 112, 114 are permanently coupled in the bridge circuit, as shown, while three respectively different valued potentiometers 116, 117, 118 are employed for balancing the bridge 104 for each of the three different colors of light provided by the lamps 56, 57, 58. The adjustable elements of potentiometers 116, 117, 118 are sequentially coupled to ground by camactuated contacts 86-6, 86-7, 86-8 which are actuated by cams 86 in sequence and respectively in syncronism with actuation of the contacts 86-2, 86-3, 86-4 which sequentially illuminate lamps 56, 57, 58. This arrangement is provided so that the output signal provided by bridge 104 will be within the same amplitude range for each color of light.

Midpoint 120 between the two photocells 70, 77 is coupled to the input circuit of a conventional amplifier 122 which has its output circuit 124 coupled to a conventional phase discriminator 126. Phase discriminator 126 is also coupled by means of leads 128 to the same 2000 cycle source as the primary winding 110 of the bridge transformer 108, phase discriminator 126 thus comparing the phase of the 2000 cycle source frequency against the phase of the output signal provided by the bridge 104.

Output circuit 130 of phase discriminator 126 is coupled to one of the input circuits of a conventional voltage comparator 132. The other input circuit 134 of voltage comparator 132 is coupled by means of cam-actuated switches 86-9, 86-10, 86-11 to the adjustable elements of three different potentiometers 136, 137, 138 respectively coupled across supply lines 140 which in turn are coupled to a suitable source (not shown) of direct current potential. Cam-actuated contacts 89-9, 86-10, 86-11 are actuated in sequence by cams '86 and again in syncronism With contacts =86-2, 86-3, 86-4 which respectively sequentially illuminate lamps 56, 57, 58. Thus, the comparision between the reference voltage applied to voltage comparator 132 by its input circuit 134 and the Voltage appearing in output circuit 130 of the phase discriminator 126 is adjusted for each different color of light, this reference voltage determining the upper and lower limits of the signals from the phase discriminator 126. Thus, if the output signal from the phase discriminator 126 is within the predetermined upper and lower limits established by the potentiometers 136, 137, 138 for each different color of light, an output indicating signal is provided in the output circuit 134 of the voltage comparator 132. The provision of an indicating signal in the output circuit 135 of the voltage comparator 132 indicates that the spectral characteristics of the light reflected from the discrete area 81 on the test bill 24 for each different color of light corresponds, within predetermined limits, to the spectral characteristics of the light reflected from the discrete area 73 of the reference bill 40.

It will be readily understood with respect to the bridge circuit 104 that the impedance of photocells 70, 77 is primarily resistive, and thus the load circuit across the secondary winding 106 of transformer 108 comprising the series-connected photocells 7'0, 77, connected in parallel with the series-connected resistors 112, 114, is likewise primarily resistive so that the alternating current voltage appearing across the secondary winding 106 will always be lagging with respect to the alternating current voltage supplied to the primary Winding 110, the phase angle decreasing as the resistance of the load circuit increases and increasing as the load resistance decreases. Since the entire load network coupled across secondary winding 106 is primarily resistive, the alternating current voltage appearing across the corners 120, and 116, 117 or 118 of the bridge 104 in response to an unbalance will be in phase with the alternating current voltage appearing across the secondary winding 106 and thus will have the same phase relationship with the primary voltage. Thus, when the resistance of photocell 77 decreases, as by receiving more light, the phase angle will decrease, and vice versa.

Referring now briefly to FIG. 6 of the drawing, the bridge circuits 104 are not balanced to provide a zero or nul output at point 120 when the photocells 70, 77 are receiving light of identical spectral characteristics, but on the contrary are balanced to provide a finite output voltageat output terminal 120 having a predetermined lagging phase relationship with respect to the phase of the voltage applied to the transformer 108. FIG. 6 shows the output characteristic of the phase discriminator 126, phase discriminator 126 providing a direct current output voltage having a predetermined polarity in response to the phase of the output voltage of the bridge 104 with reference to the phase of the reference voltage 110, 128. In the illustrated and preferred embodiment, phase discriminator 126 provides a positive direct current output voltage in response to the lagging alternating current output voltage of bridge 104, the magnitude of the direct current output voltage increasing as the lagging phase displacement increases in response to reduced resistance of the bridge, as above-described. Thus, when the phase and magnitude of the output voltage of bridge 104 indicates that the spectral characteristics of the light received by photocells 77 are within the desired range of the acceptance, phase discriminator 126 provides a positive direct current output voltage in its output circuit 130, as shown at 142 in FIG. 6. Reference direct current voltages, respectively established by otentiometers 136, 137 and 138 are applied to input circuit 134 of voltage comparator 130, which com-pares the applied direct current reference voltage with the direct current voltage applied to its other input circuit 130 from phase discriminator 126. Thus, when the direct current output voltage from the phase discriminator is within the predetermined range of acceptance 142, i.e. deviating from the direct current reference voltage by no more than the limits of acceptance range 142, a direct current acceptance signal is provided by voltage comparator 132 in its output circuit 135. It will be understood that the three different potentiometers 136, 137, 138 sequentially selected by the cam-actuated switches 86-9, 86-10, 86-11 determine the width of the range of acceptance 142 for each different color.

It will now be seen that an indicating signal is provided in output circuit 135 of voltage comparator 132 when each of the signals in output circuit 130 of phase discriminator 126 is within predetermined limits. Thus, when the spectral response of the area 81 on the test bill 24 to each of the three sequentially flashed colors of light is within limits, three sequential indicating signals will be provided in output circuit 135 of voltage comparator 132. However, as for example when the response to the pink lamp 56 is outside of the predetermined limits, no indicating signal will be provided during the interval when cam-actuated switches 86-3 and 86-10 are closed.

It will be readily understood that other conventional circuitry may be employed for providing indicating signals when the spectral response of each area of the test bill for each color of light is within predetermined limits.

The output circuits 135 of the voltage comparators 132 of the three discriminator channels A, B, C are respectively coupled to conventional logic relays 136, 138, 140. Logic relays 136, 138, 140 sense the sequential presence of three indicating signals in each of the output circuits 135, thus indicating that the spectral response of each of the discrete areas 81, 82, 83 of the test bill 24 to each of the three colors of light sequentially provided by lamps 56, 57, 58 is within the predetermined limits, and provide an output indicating signal in output circuit 142. Output circuit 142 has operating coil 144 of validation relay 146 coupled in series therewith, and thus if three indicating signals are provided in each of the three output circuits 135, operating coil 144 is energized. Validation relay 146 is provided with contacts 146-1 coupled in series with the grabber solenoid 50 and thus the presence of the output indicating signal in output circuit 142 of the logic relays 136, 138, 140 will result in energization of grabber solenoid 50 and actuation of the grabber assembly 44 to remove the thus-validated test bill 24 from the slide 20.

Validation relay 146 is provided with another set of contacts 14'6-2 serially connecting output circuit 102 of the empty tray sensor amplifier 100 to solenoid 148 of the change-making and/or vending apparatus (not shown). Thus, energization of operating coil 144 of validation relay 146 indicating that each of the discrete areas 81, 82, 83 of the test bill 24 provides the proper spectral response to each of the three colors of light results in closing of contacts 146-2. As above-described, at the end of the dwell period during "which slide is held stationary in its inspection position, the slide is moved forward toward its loading position by motor and the ultraviolet lamp 58 is flashed on with increased brilliance by actuation of cam-actuated contact 86-5. If then the grabber mechanism 44 has successively removed the validated bill from the recess 22 of the slide 20, empty tray sensor photo cell will provide an output signal in response to sensing the empty recess 22 of slide 20 and the vend solenoid 148 Will be energized. It will readily be seen that if the test bill has not been validated, i.e., one or more of the discrete areas 81, 82, 83 did not provide the proper spectral response to one or more of the three colors, validation relay 146 will not be energized and its contacts 146-2 will not be closed so that the vend solenoid 148 cannot be energized. Further, if the bill has been validated resulting in closing of contacts 146-2, but if the grabber assembly 44 does not remove the validated bill from the recess 22 in the slide 20, empty tray sensor photocell 85 will not generate an output signal and the vend solenoid 148 will not be energized.

Referring now briefly to FIG. 5, one conventional form of solid state logic relay circuit is shown which may be employed for each of the logic relays 136, 138, 140. Here, output circuits of voltage comparator 132 is coupled to the input circuit of a first bistable multivibrator 150 which has its output circuit 152 coupled to one of the input circuits of AND gate 154, the other input circuit of AND gate 154 being coupled to the output circuit 135 of the comparator 132. The output circuit 156 of AND gate 154 is coupled to the input circuit of a second bistable multivibrator 158 which has its output circuit 160 coupled to one of the input circuits of AND gate 162, the other input circuit of AND gate 162 likewise being coupled to the output circuit 135 of comparator 132. Output circuit 164 of AND gate 162 is coupled to the input circuit of a third bistable multivibrator 166 which has its output circuit 168 coupled to one of the input circuits of AND gate 170 along with the output circuits from the two other logic relay circuits 138, It will be seen that the presence of the first indicating signal in output circuit 135 in response to flashing of lamp 56 will actuate the first bistable multivibrator to provide an output signal in its output circuit 152. Application of the second indicating signal in output circuit 135 in response to the flashing of the second lamp 57 to the AND gate 154 together with the output signal in output circuit 152 will provide an output signal in output circuit 156 which actuates the second bistable multivibrator 158 to generate an output signal in output circuit 160. Application of the third indicating signal in output circuit 135 in response to flashing of the third lamp 58 to the AND gate 162 along with the output singal in output circuit will provide an output signal in output circuit 164 which actuates the third bistable multivibrator 166 to provide an output signal in output circuit 168 which is applied to the AND gate 170. Application of output signals from the other two logic relays 138, 140 to the AND gate results in the provision of the output indicating signal in the output circuit 142.

In order to reset the bistable multivibrators 150, 158', 166 at the end of one validation cycle, cam-actuated con tacts 86-12 couple the reset input circuits 172, 174, 176 of the bistable multivibrators 150, 158, 166 to a suitable source of potential 178 during return of the slide 20 from its inspection position to its loading position. It will be readily understood that other conventional logic relay sys tems employing solid state devices or electromagnetic relays may be employed for sensing the sequential provision of three indicating signals in the output circuits 135 of the voltage comparators 132 of each of the three channels A, B, and C, and providing an output .indicating signal in response thereto.

In a specific embodiment of the invention employing the above-referred to F6-T5 pink, green and near ultraviolet fluorescent lamps, Clairex No. 705HL photocells were employed for the two groups 62, 64; however, other conventional broad band photosensitive devices may be employed. It will be seen that with the provision of a plurality of sensors each responsive to a preselected discrete area of the reference and test bill and the use of a plurality of sequentially illuminated light sources each providing light in a different color spectra or section, a multiplicity of comparisons are made between the test bill and the reference bill. Thus, in the illustrated embodiment in which the groups 62, 64 each comprise three sensors and three different colored lamps are employed, a total of nine comparisons are made between the test bill and the reference bill, thus providing highly accurate discrimination between genuine and foreign and/or counterfeit currency. The narrow band light sources employed in this invention are readily available in a wide range of color spectra or sections and furthermore, relatively broad band photocells are relatively inexpensive and have low impedance characteristics which lend themselves to use with transistorized amplifier and logic circuitry, thus pro- Viding greatly increased life and reliability.

Referring now to FIG. 7 of the drawing, there are shown amplitude response curves provided by the apparatus of the invention with near ultraviolet, green and pink lamps, for specific left, center and right discrete areas of United States one, five and twenty dollar bills, one specific type of play money, and the five peso note. It will be seen that the amplitude response readings for each of the three areas may be tabulated from FIG. 7 as fol- It will be seen that for validation of a United States one dollar bill, the reference amplitude response readings are:

Left 34-5 9-5 3 Center 46-69-65 Right 37-5 6-49 It has been found that a tolerance of plus-or-minus three percent (3%) may be allowed in order to accept brand new or dirty currenecy while still rejecting counterfeit currency or foreign currency or currency of the wrong denomination. Thus, the acceptable range of response readings for a United States one dollar bill are:

Left Center Right Low limit 31-56-50 43-66-62 34-53-46 High limit 37-62-56 49-72-68 40-59-52 It will now be seen that the five peso note and United States twenty dollar bill will provide amplitude response readings of:

Left Center Right peso 33-51*-46* 43-66-63 33*-48*-44* U.S. 36-61-55 39*-60*-55* 3965*-60* The out-of-limits responses indicated by will reliably reject these currencies. It will thus be seen that while the spectral response of a given piece of currency being discriminated against may be within limits for any given area and for any given color of light, by determining the spectral response of a plurality of spaced-apart discrete areas to a plurality of different colors of light, highly accurate discrimination is obtained.

While the discrete areas viewed on the test and reference bills are shown as being spaced-apart, there are instances where it may be desirable to have the areas touch or even partly overlap in order to obtain maximum differentiation from other denominations of bills likely to be offered. It will further be understood that compensation for such variables as voltage, light intensity and temperature can be provided by known circuitry and components and thus, with such arrangements, the employment of a reference bill may be eliminated.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of this invention.

What is claimed is:

1. The method of discriminating between desired and undesired documents comprising the steps of: sequentially illuminating one surface of a document to be inspected with a plurality of different colors of light, one at a time; sequentially developing a plurality of electrical signals respectively responsive to the spectral content of the light of each different color reflected from a plurality of discrete areas on said one s rface; and utilizing all of said signals to develop an indicating signal when the spectral response of each of said discrete areas to each of said colors corresponds to that of a desired document.

2. The method of discriminating between desired and undesired documents by spectral analysis of light reflected therefrom comprising the steps of: successively emitting light in a predetermined plurality of intervals, each successive light emission being in a different color section; exposing one surface of a document to be inspected to said successive light emissions while holding said document stationary with respect thereto and reflecting each said successive light emission therefrom; receiving at a plurality of locations light respectively reflected during each successive light emission from a plurality of preselected discrete areas of said one surface; developing a plurality of electrical signals having amplitudes respectively responsive to the spectral content of the light received from said discrete areas during each successive light emission; and utilizing all of said signals to develop an indicating signal when the spectral content of the light reflected from each of said discrete areas during each of said successive light missions corresponds to that provided by a desired document.

3. The method of claim 2 wherein at least three successive light emissions are provided, and wherein said color sections include color components existing on said one surface of a desired document.

4. The method of claim 2 wherein at least three successive light emissions are provided, at least two of said color sections being in the visible light range.

5. The method of claim 2 wherein said color sections are discretely different and respectively narrow band.

6. The method of discriminating between desired and undesired documents by spectral analysis of light reflected therefrom comprising the steps of: providing a plurality of light sources respectively having narrow band light emission in discretely different color sections; successively illuminating one surface of a document to be inspected with light respectively emitted by each one of said sources, one at a time, while holding said document stationary with respect to said sources and reflecting said light from said surface during said successive illuminations; receiving at a plurality of locations light respectively reflected during each successive illumination from a plurality of preselected discrete areas of said one surface; developing a plurality of electrical signals having amplitudes respectively responsive to the spectral content of the light received from said discrete areas during each successive illumination; detecting the amplitudes of each of said signals during each successive illumination to determine whether said signals are respectively within predetermined limits; and developing an indicating signal in response to each of said signals being Within said limits during each of said illuminations.

7. The method of claim 6 wherein said color sections are respectively in the near ultraviolet, green and near red regions of the spectrum.

8. The method of claim 6 comprising the further step of establishing respectively different limits for each said successive illumination.

9. The method of discriminating between desired and undesired documents by spectral analysis of light reflected therefrom comprising the steps of: providing a plurality of light sources respectively having narrow band light emission in discretely different color sections; simultaneously exposing corresponding surfaces of a test document to be inspected and a reference document to said sources While holding said documents stationary With respect thereto; successively illuminating both of said documents with light respectively emitted by each one of said sources, one at a time, and reflecting said light from said surfaces during said successive illuminations; receiving at a first plurality of locations light respectively reflected during each successive illumination from a plurality of preselected spaced-apart discrete areas of said surface of said reference document; developing a first plurality of electrical signals respectively responsive to the spectral content of the light received from said discrete areas of said reference document during each successive illumination; receiving at a second plurality of locations light respectively reflected during each successive illumination from a plurality of discrete areas of said surface of said test document respectively corresponding in location to said discrete areas of said reference document; developing a second plurality of electrical signals respectively responsive to the spectral content of the light received from said discrete areas of said test document during each successive illumination; comparing corresponding ones of said first and second plurality of signals and developing a third plurality of electrical signals having amplitudes respectively responsive to the difference between the spectral content of the light received from said discrete areas of said test document and the spectral content of the light received from corresponding discrete areas of said reference document during each successive illumination; detecting the amplitudes of each of said third plurality of signals during each said successive illumination to determine Whether said last-named signals are respectively within predetermined limits; and developing an indicating signal in response to each of said third signals being within said limits during each of said successive illuminations.

10. Apparatus for discriminating between desired and undesired documents by spectral analysis of light reflected therefrom comprising: means for sequentially emitting a plurality of different colors of light, one at a time; means for receiving a doucment to be inspected and for holding the same in stationary relationship with respect to said light emitting means with one surface exposed thereto so as to receive light therefrom; a plurality of light-sensitive means for respectively developing electrical signals having amplitudes responsive to the spectral content of light received thereby; said light-sensitive means being disposed to receive light reflected from a plurality of preselected discrete areas of said one surface thereby respectively to develop said signals in response to the spectral content of the light reflected from each of said discrete areas during each of said sequential light emissions; and means for analyzing each of said signals during each of said light emissions and including means for developing an indicating signal when the spectral content of the light reflected from each of said discrete areas during each of said sequential light emissions corresponds to that provided by a desired document.

11. The apparatus of claim 10 wherein said light emitting means comprises a plurality of light sources each emitting light in a different color section, and means for sequentially illuminating said light sources one at a time.

12. The apparatus of claim 11 wherein there are at least three of said light sources, and wherein said color sections include color components existing on said one surface of a desired document.

13. The apparatus of claim 11 wherein said color sections are discretely different and respectively narrow band.

14. The apparatus of claim 11 wherein there are at least three of said light sources and said color sections are respectively in the near ultraviolet, green and near red regions of the spectrum.

15. The apparatus of claim 10 wherein said analyzing means includes means for determining Whether each of said signals is within predetermined limits during each of said sequential emissions, and means for developing said indicating signal in response to each of said first-named signals being within said limits during each of said sequential emissions.

16. The apparatus of claim 15 further comprising means for establishing different limits during each of said sequential emissions.

17. Apparatus for discriminating between desired and undesired documents by spectral analysis of light reflected therefrom comprising: a plurality of light sources each emitting light in a descretely different narrow band color section; means for sequentially illuminating said light sources, one at a time; means for receiving a. document to be inspected and having an inspection position for holding said document in stationary relationship with respect to said light sources with one surface exposed thereto so as to receive light therefrom; means defining a plurality of discrete areas on said one surface of said document, said areas being respectively relatively small compared with the total area of said one surface; a plurality of lightsensitive means for respectively developing electrical signals having amplitudes responsive to the spectral content of light received thereby; said light-sensitive means being respectively disposed to receive light reflected from said discrete areas thereby respectively to develop said signals in response to the spectral content of the light reflected from each of said discrete areas during each of said sequential illuminations; means for determining whether each of said signals is Within predetermined limits during each of said sequential illuminations; and means for developing an indicating signal in response to each of said first-named signals being Within said limits during each of said sequential illuminations.

18. The apparatus of claim 17 further comprising means for moving said receiving means between a loading position and said inspection position; and means responsive to said moving means for actuating said sequential illuminating means when said receiving means is in said inspection position.

19. The apparatus of claim 17 further comprising means responsive to said sequential illuminating means for providing different predetermined signal limits during each said sequential illumination.

20. Apparatus for discriminating between desired and undesired documents by spectral analysis of light reflected therefrom comprising: a plurality of light sources each emitting light in a discretely different narrow band color section; means for sequentially illuminating said light sources, one at a time; means for receiving a document to be inspected and having an inspection position for holding said document in stationary relationship With respect to said light sources with one surface exposed thereto so as to receive light therefrom; means for holding a reference document in stationary relationship with respect to said light sources with one surface exposed thereto so as to receive light therefrom; first and second pluralities of light-sensitive means for respectively developing first and second electrical signals having amplitudes responsive to the spectral content of light received thereby; said first plurality of light-sensitive means being disposed respectively to receive light reflected from a first plurality of discrete areas on said one surface of said document to be inspected thereby respectively to develop said first signals in response to the spectral content of the light reflected from each of said first discrete areas during each of said sequential illuminations; said second plurality of light-sensitive means being disposed respectively to receive light reflected from a second plurality of spaced-apart discrete areas on said one surface of said reference document having locations corresponding respectively to the locations of said first discrete areas thereby respectively to develop said second signals in response to the spectral content of the light reflected from each of said second discrete areas during each of said sequential illuminations; means for comparing corresponding ones of said first and second signals thereby to develop third signals having amplitudes respectively responsive to the difference between the spectral content of the light reflected from said first and second discrete References Cited UNITED STATES PATENTS 3,122,227 2/1964- Bookout et a1. 209-l1l.6 X 3,220,549 11/1965 Wong 209-111.6 Re. 26,176 3/1967 Steiner 250219 X 3,356,992 12/1967 Ptacek et al. 250 219 X RALPH G. NILSO'N, Primary Examiner T. N. GRIGSBY, Assistant Examiner US. Cl. X.R.

l94-4; 209-1ll.6; 2502l4, 217, 220; 340-449;

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,480,785 November 25, 1969 Don R. Aufderheide It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 37, "currecny" should read currency Column 2, line 42, "now" should read not line 48, "horiozntally" should read horizontally Column 5, line 39, "flshing" should read flashing Column 6, line 13, "89-9" should read 86-9 lines 16 and 17, "comparision" should read comparison line 56, "decrease" should read increase Column 7, line 75, "successively" should read successfully Column 8, line 19, "circuits" should read circuit line 47, "singal" should read signal Column 9, line 57, "currenecy" should read currency Column 10, line 52, "missions" should read emissions Column ll, line 61, "doucment" should read do'ument Column 12, line 31,

, "descretely" should read discretely Signed and sealed this 4th day of August 1970.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, JR.

Attesting Officer Commissioner of Patents 

